Stringent emission standards have increased the heat rejection requirements of diesel engine cooling systems. As a result more efficient means of cooling these engines are required. Windrowers operate in high crop debris conditions that foul cooling systems. Increasing the cooling requirements requires more air flow through the coolers, which results in either higher velocity air given the same area, or larger cooler face with equal or reduced air velocities. Historically the cooling system in windrowers had the heat exchangers set up in series, i.e. with the discharging air stream from one heat exchanger forming the inlet air stream of a next heat exchanger, significantly reducing their overall efficiency. The most efficient heat exchanger has a large frontal surface area and a thin core exposed to ambient air.
John Deere, New Holland and the current production MacDon Windrower all use similar systems that draw the cooling system air in at the rear of the machine, through a series of heat exchangers, exhausting the hot air into the direction of travel in which the machine is driven while operating in the field (heavy loading so where cooling requirements are the highest. Such conventional arrangement is schematically illustrated in FIG. 1, where a windrower tractor 1 is being driven in a forward working direction F, in which the header 23A of the windrower 1 leads a frame 11 on which the operator cabin 30, engine 24, and heat exchangers 50a, 50b are carried. The engine 24 lies between the operator cab 30 and the heat exchangers 50a, 50b, which are mounted one behind the other at the rear of the tractor frame. The rearmost mounted heat exchanger 50a draws ambient air 52 in from behind the tractor for cooling one or more engine associated fluids (e.g. coolant, engine oil, engine charge air), and the air then continues forwardly through the second heat exchanger 50b to cool another one or more of the engine associated fluids. The intake air of the second heat exchanger 50b, being the same air discharged from the first heat exchanger 50a, is thus at a higher temperature than the ambient air used by the first heat exchanger.
This conventional configuration drawing in air for the cooling system at the rear of the machine and exhausting the hot air towards the front of the machine (i.e. in the direction of travel) acts to preheat the air being drawn into the system. That is, the forward discharge of the exhaust 54 air from the heat exchangers 50a, 50b creates an issue in that the forward working direction F of the machine moves the tractor forwardly past freshly exhausted air 54, which means that some of this exhaust air 54 is re-circulated through the heat exchangers, as shown in broken lines at 56, thus reducing the inlet air temperature and accordingly reducing the efficiency of the heat exchanger operation.
One known Hesston windrower, shown schematically in FIG. 2, differs from the above configuration, instead having the heat exchangers 18a, 18b positioned between the cab 14 and the engine to draw the ambient air 20 in behind the cab 14 on top of the engine hood 58, and then discharge the exhaust air 22 downwardly. However the majority of heat exchangers 18a, 18b or coolers in this configuration are still arranged in series.
A more recent Hesston design is shown schematically in FIGS. 9 and 10. This design employs parallel heat exchangers arranged in a box like configuration behind the engine, with two heat exchangers 50x-1 and 50x-2 facing rearward and two others 50y, 50z facing laterally outward. Ambient air 52 is drawn forwardly and laterally in at the rear of the machine by a fan 59 that is located opposite the rear heat exchangers 50x-1, 50x-2 and between the two lateral heat exchangers 50y, 50z, the air thus passing through heat exchangers 50x-1, 50x-2, 50y and 50z and then being discharged forwardly towards the engine before exiting laterally and downwardly from the engine compartment. While the use of parallel streams of intake air for the different heat exchangers presents some advantage over more conventional series configurations, the direction of exhaust air discharged from the heat exchangers again creates potential air recirculation paths 56 that may limit the heat exchange efficiency.
Accordingly, there is desire to provide an improved cooling system for the engine of a windrower or swather tractor.